TWENTY people have died in a cholera outbreak in Kano, northern Nigeria, in the past three weeks, health workers said in Lagos on Monday. The humanitarian organisation Medecins Sans Frontieres, which has set up a treatment centre in the city, has seen some 350 cases of cholera since March 24 around Kano, one of the host cities for the FIFA World Youth Championship. Authorities have been anxious not to generate publicity for fear of alarming visitors coming to Nigeria for the event, a local government health official said.